When taking a photo, especially a portrait of a person of group of people, it is often desirable to deliberately blur the background. This is usually done for aesthetic effect—to make the people stand out better and to help hide distracting or undesirable backgrounds.
Creating a photo with maximum background blurring will also aid a subsequent image processing task of removing the background so that a different background can be substituted. Background removal techniques include edge and gradient analysis; maximum background blurring helps this analysis by removing or softening edges in the background, thus reducing the number of edges to follow and making the key edges of interest, namely those around the foreground subject, easier to find and follow.
Generally speaking, the depth of field is the distance in front of and behind the subject that appears to be in focus. Accordingly, items outside the depth of field, e.g., background, are not in focus, i.e., are blurry. It is well known by skilled photographers that there are a set of techniques that can be used to control the depth of field in an image and therefore to control the blurring of the background. One such technique involves adjusting the aperture setting—the larger the aperture the smaller the depth of field. Some cameras have a portrait mode that sets the camera to use a wide aperture.
Another technique to control the depth of field in an image involves the focal length and the subject distance. Longer focal lengths (corresponding to more powerful zoom settings) produce smaller depths of field. Moving towards the subject achieves roughly the same effect and is complimentary. Both techniques can be used in combination—when the subject fills more of the viewfinder the depth of field is reduced. Thus, the photographer can use a higher zoom or move closer to the subject or do a combination of these to enlarge the subject in the viewfinder and decrease the depth of field.
These techniques require the user to be a somewhat sophisticated photographer to carry them out successfully to enhance background blurring. Moreover, in some cases, the background is too close to the subject to allow for adequate blurring while maintaining the subject in focus. In other words, the depth of field cannot be set small enough to cover only the subject without any portion of the background. As discussed above, depth of field depends on variables that may or may not be entirely controllable by the user. For example, the level of zoom used is, to some degree, dependent on the distance to the subject, which may not always be controllable by the user.
Accordingly, there exists a need for methods, systems, and computer program products for providing background blurring when capturing an image using an image capture device.